1. Field of the Invention
This invention relates to the field of polymerization catalysts for polyurethanes.
2. Description of the Prior Art
Numerous catalysts and catalyst systems for the polyurethane reaction are known.
The polyurethane polymerization technique of the "one-shot" type for the manufacture of urethane elastomers generally comprises reacting a hydroxyl-terminated polyether diol or hydroxyl terminated polyester diol of about 2,000 molecular weight, a bifunctional extender and an organic diisocyanate in the presence of a basic amine catalyst such as triethylenediamine (DABCO), an organometallic catalyst such as tin acylate, dibutyltin diacylate or phenyl mercuric acylate, or blends of these and similar catalysts.
The same catalysts and catalyst systems can be employed for the polymerization technique of the "prepolymer" type in which a prepolymer derived from the reaction of the aforedescribed diols with an excess of an organic diisocyanate to provide terminal isocyanate groups thereon is reacted with a bifunctional extender.
Typically, these catalysts and catalyst blends provide gel times of under 1 minute, and generally, under thirty seconds. For certain types of polyurethane polymerization processes, in particular, for the liquid injection molding of polyurethane elastomers, it is often highly desirable to employ a catalyst or catalyst system which results in gel times well in excess of one minute.